Suspended staging type welding machine

ABSTRACT

A single cable type suspended staging is guided for vertical travel along plate members being welded together by coplanar, vertically spaced apart guide wheels. The guide wheels run in the gap between the members and are each spring biased towards the work surface. Two electroslag form shoes are supported from the staging below the guide wheels. Each shoe is independently spring biased into contact with its side of the plate members. One or more tensioned hold-in lines hold the staging inwardly against the plate members. Each hold-in line rides on a sheave which is automatically controlled to move either towards or away from the object for the purpose of maintaining proper tension in the holdin line.

United States Patent Fisher [4 June 20, 1972 [54] SUSPENDED STAGING TYPE WELDING 3,220,509 11/1965 Fisher ..1s2/142 MACHINE 2,689,890 9 1954 Green ..1s2/142 [72] Inventor: Sidney L. Fisher, Renton, Wash. p i Truhe 73 Assi nee: s ider $111 in Inc., Seattle, w h. 14mm 1368" 1 g p g as Attorney-Graybeal, Cole & Barnard [22] Filed: Dec. 10, 1970 211 Appl. No.: 96,757 [57] ABSTRACT A single cable type suspended staging is guided for vertical Related Applicauon Data travel along plate members being welded together by [63] C(mtinuafiomimpan of 861,757, Sept 29, coplanar, vertically spaced apart guide wheels. The guide 1969 wheels run in the gap between the members and are each spring biased towards the work surface. Two electroslag form 52 [1.8. CI. ..219 12s R 182/142 Sims are Su10mm mm the aging be1w the guide Wheels- I 51 Int Cl D D 23k 9/12 Each shoe is independently spring biased into contact with its f s g side Of the plate members. One or more tensioned hold-in lines hold the staging inwardly against the plate members.

Each hold-in line rides on a sheave which is automatically con- [56] References Clted trolled to move either towards or away from the object for the UNITED STATES PATENTS purpose of maintaining proper tension in the hold-in line 3,382,344 5/1968 Hasegawa et a1. ..2l9/125 X 11 Claims, 11 Drawing Figures 20 a 3g- 7 w 3;, 1 1 PM; 1 1 1 '1 41 1 -1 \I o 1 1 1i /d v 1 /75 1 11 I 1 E L l /20 iii Patented June 20, 1972 3,671,712

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ZIW, i gm Q SUSPENDED STAGING TYPE WELDING MACHINE CROSS REFERENCE TO RELATED APPLICATIONS This is a continuation-in-part of my copending application Ser. No. 861,757, filed Sept. 29, 1969, and entitled Suspended Staging Type Automatic Welding Machine.

BACKGROUND OF THE INVENTION 1 Field of the Invention This invention relates to an automatic welding machine, and more particularly to an improved electroslag welding machine for welding elongated vertical straight or curved seams.

2. Description of the Prior Art In ship building, large tank construction, etc., vertical walls or barriers are formed by welding together a plurality of large plate steel panels. Automatic welding machines are generally used for performing this work. Examples of known vertical seam automatic welding machines can be found in U.S. Pat. No. 2,794,901, issued June 4, 1957 to Lynn J. Christensen et al.; in U.S. Pat. No. 3,210,520, issued Oct. 5, 1965 to Perry C. Arnold et al.; in U.S. Pat. No. 3,382,344, issued May 7, 1968 to Hasegawa et al.; in U.S. Pat. No. 3,419,700, issued Dec. 31, 1968 to Tanigaki et al., in U.S. Pat. No. 3,436,518, issued Apr. 1, 1969 to Knut A. W. Persson; in U.S. Pat. No. 3,436,519, issued Apr. 1, 1969 to Arnold Weisselberg et al., in U.S. Pat. No. 3,437,786, issued Apr. 8, 1969 to Rene D. Colinet et al.; and in U.S. Pat. No. 3,453,411, issued July 1, 1969 to Van Noyen.

The present invention relates to improvements in automatic vertical seam welding machines, and in particular to the provision of improved guidance and support apparatus for the welding equipment, and to an improved system for maintaining the welding machine in proper position against the article being welded, enabling the machine to better perform its welding function while traversing generally vertical surfaces, including irregular and vertically curved as well as vertically straight surfaces.

SUMMARY OF THE INVENTION According to the present invention, the welding equipment is supported on or carried by a single cable supported staging. The rate of climb of the staging is regulated to correspond to the rate of travel requirements of the welding equipment. During its vertical travel the staging is maintained in against the members being welded by means of one or more hold-in cables which may be similar to the type shown in my U.S. Pat. No. 3,220,509, granted Nov. 30, 1965, or the type shown in my aforementioned U.S. application Ser. No. 861,757.

One aspect of the present invention is to combine a motorized means for automatically maintaining the proper tension or hold-in force in each hold-in cable with a guidance and support system for electroslag welding equipment which adapts such equipment for following curved and/or irregular surfaces as well as substantially vertically straight surfaces. Another aspect of the invention relates to the provision of an improved support system for electroslag welding equipment which is usable with several types of vertical seam welding machines.

BRIEF DESCRIPTION OF THE DRAWING vertical seam being welded from the welding machine side of the work material;

FIG. 5 is a fragmentary view in the region of the guide slot, showing the periphery of the guide wheel engaged in such slot;

FIG. 6 is a fragmentary elevational view of one of the resiliently mounted guide wheel assemblies for the welding machine;

FIG. 7 is a somewhat diagrammatic side elevational view of the electroslag welding and guide wheel parts of the machine shown in one position of travel along an uneven vertical surface;

FIG. 8 is a view similar to FIG. 7, but showing the machine at a different position on the surface;

FIG. 9 is a top plan view of one of the hold-in cable tensioning mechanisms, with some outer parts thereof broken away for clarity of illustration of certain inner parts, with a constant section intermediate portion of the mechanism being segmented, and with certain end portions of the mechanism not essential to the showing being omitted;

FIG. 10 is a side elevational view of the mechanism of FIG. 9, which in similar fashion is also segmented and broken away in parts; and

FIG. 11 is a fragmentary side elevational view of the control cam end of the hold-in mechanism.

DETAILED DESCRIPTION OF THE INVENTION Referring to FIGS. 1 and 2, the welding machine is shown to comprise a suspended staging 10 having a forwardly disposed operator compartment or cage 12. Compartment 12 includes an operators seat 14 and a floor or deck 16. A suspension line or cable 18 extends from an anchored overhead position (not shown) downwardly through a fairlead 20 to a power-driven winch drum 22 on to which the suspension line 18 is wound. By way of typical and therefore non-limitive example, the winch 22 may be of the level-winding type disclosed and claimed in my prior U.S. Pat. No. 2,998,094.

Winch drum 22 is preferably driven by a variable speed, reversible electric motor mounted in the lower portion of the staging l0, closely adjacent the winch drum 22 and suitably connected thereto by gear reduction means. The control circuit for the electric drive motor includes a suitable switch mechanism operable to control the direction of rotation of the reversible motor. Preferably, a rheostat is provided in series between the switch mechanism and the motor and is used for varying the rotational speed of the motor and the winch drum 22, so as to in turn vary the rate of up or down travel of the staging 10. The rheostat may be adjusted so as to coordinate the rate of upward movement of the staging with the speed at which the welding operation can be performed. A foot operated off-on switch (not shown) may be provided forcontrolling the electric motor and hence the starting and the stopping of vertical travel. Reference is made to my U.S. Pats. Nos. 2,998,094 and 3,303,321 for a detailed discussion of suitable staging drive and level winding equipment.

The welding machine must be accurately guided during its vertical travel. According to the invention the narrow gap which exists between the two sections of plate material being welded together is used as a guide track, as will hereinafter be explained in greater detail.

It is also important for the welding machine to be maintained in close against the plate members 24, 26. For this purpose a pair of hold-in cables 28, 30 are provided, one on each side of the staging 10. The cables 28, 30 are suitably anchored at their upper and lower ends and they each ride in a rearward peripheral groove portion of a freely rotatable sheave type bearing 32. The sheaves 32 are supported by a mechanism which is adapted to automatically shift the sheaves 32 in position normal to the members 24, 26, for the purpose of maintaining ample tension in the hold-in lines 28, 30.

As best shown by FIGS. 3 and 9,- each sheave assembly is individually securable to a frame portion of the staging 10 on its side of the staging 10. The particular staging illustrated comprises a pair of rearwardly located vertical frame posts 34, one on each side of the staging 10. Each sheave mechanism includes an elongated lead screw housing 36 and a plurality of mounting clamps 38. The mounting clamps 38 are shown to be in the form of U-shaped pieces of metal having one leg thereof welded to the back wall of the lead screw housing 36. Machine bolts 40 or the like extend between the two legs of the clamp member and when tightened serves to pull them together in clamping engagement with the frame post 34. The rear clamp 38 is similarly secured to a rear frame post 42.

Referring now to FIGS. 9 and 10, a compression spring 44 is located in each lead screw housing 36 near the ends thereof closest to the front of the staging 10. A lead screw 46 is located inside of housing 36 and it includes a head portion 48 which is in contact with the compression spring 44. As shown by FIGS. 1 and 10, the outer side of the lead screw housing 36 includes a longitudinal slot 50. An elongated sheave support block 52 is located within the housing 36. Block 52 includes a longitudinal bore which is internally threaded and the threads match the external threads of the lead screw 46. Block 52 is transversely dimensioned to be slightly smaller in size than the transverse dimension of the hollow interior of the housing 36. A plate 54 (FIG. 9) is located outwardly of the housing 36 and is secured to the block 52, such as by counter-sunk metal screws 56, or the like. The sheave 32 is rotatably mounted by axle means carried by the plate 54. As can be readily seen, rotation of the lead screw 46 causes movement of the block 52 in one direction or the other, longitudinally along the lead screw 46, resulting in a longitudinal travel of the sheave 32 relative to the lead screw housing 36.

A motor mounting bracket 60 is connected to, and depends downwardly below, and then endwise outwardly from the end portion of lead screw housing 36 which is closest to the rear of the staging 10. This bracket 60 mounts an electric motor 62 which serves to rotate the lead screw 46. The end of the lead screw 46 distal the spring 44 is connected to a circular plate 64 (FIGS. 9-11) in such a fashion that the plate both rotates and moves axially with the lead screw 46. As shown by FIG. 11, the lead screw 46 is secured to the inner end of a tubular hub 66 to which the plate 64 is secured. The output shaft 68 of the motor 62 is non-circular in cross section, or is provided with a key. It is snugly received within a blind socket 70 formed axially through hub 66 and having essentially the same cross-sectional shape as shaft 68. The non-circular cross-sec tional shapes of the shaft 68 and the complementary socket 70 establishes a rotary drive connection between the shaft 68 and the hub 66. The fit of shaft 68 is loose enough within socket 70 so that the hub 66 is free to slide longitudinally of the shaft 68.

Each motor 62 is a reversible motor and it is provided with both manual and automatic control means. The manual control means is primarily used when it is desirable to slacken the hold-in lines 28, 30, for the purpose of dismantling the equipment, or to initially tension the lines 28, 30.

The automatic control mechanism includes a control arm 72 which is pivotally mounted at a point intermediate its ends for swinging movement in a plane perpendicular to the plane of the plate 64, such as by a pivot pin 74. As shown by FIG. 11 the lower end of arm 72 is bifurcated and places an arcuate finger 76, 78 on each side of the plate 64. The fingers 76, 78 are inwardly concave to provide clearance for the peripheral portion of the plate 64 during each stage of relative movement. The opposite or upper end 80 of arm 72 carries an arcuate segment 82 of a gear which meshes with a drive gear 84 which is located at one end of an elongated cam shaft 86 mounted to turn on an axis which is parallel to the axis of pivot pin 74. A plurality of switch operating earns 88, 90, 92, 94 are spaced apart along the shaft 86. Each cam 88, 90, 92, 94 includes a mounting hub portion and a plate portion which is a sector of a circular plate (FIG. 11). Set screws extend through the hubs and secure the cams 88, 90, 92, 94 in predetermined positions relative to each other on the shaft 86. The plate portions of the cams 88, 90, 92, 94 are positioned to each contact and close a related switch lever 96, 98, 100, 102 during a particular rotational phase of the cam shaft 86.

The springs 44 are calibrated springs and each stores a predetermined amount of energy, i.e. 600 pounds. Let it be assumed that the various components are in the position depicted by FIG. 10, the tensioning mechanism is on automatic and a tension deficiency suddenly develops in a hold-in cable 28, 30. In such a situation the stored energy in spring 44 would push the lead screw 46 to the right, as pictured. The lead screw 46 would carry with it the cam positioning plate 64. Through arm 72, segment gear 82, gear 84 and shaft 86, the plate 64 would position one of the cams (e.g. cam 94) into contact with the switch lever 102 of the related switch, closing such switch. This would control motor 64 to rotate in the direction causing lead screw 46 to rotate in the direction causing block 52 and the sheave 32 carried thereby to be moved rearwardly from the plate members 24, 26 and against the hold-in line 28 or 30, bending such line outwardly and increasing its tension. Once the tension in line 28 or 30 reaches a desired amount further outward travel of the sheave 32 is arrested and the lead screw 46 begins to move longitudinally inwardly towards plate 24, 26, compressing spring 44. Lead screw 46 carries plate 64 with it as it so moves. This plate movement causes a clockwise rotation of arm 72 and counterclockwise rotation of the gear 84, the shaft 86 and the cam members 88, 90, 92, 94 carried thereby. Once the cable 28 or 30 is sufficiently tensioned one of the other cams (e.g. 92) operates its switch lever to open the motor control circuit. Switches 96, 98 are in the manual circuit and are limit switches to control the maximum allowable inward and outward movement of the sheave 32 during manual operation.

The tension control mechanisms for the two hold-in lines 28, 30 operate independently of each other. This is important since an irregular wall shape or some other factor might cause a different set of conditions affecting hold-in line tension on one side of the staging 10 from those existing on the other side of the staging 10.

The basic welding equipment of the illustrated embodiment is old per se. It is of the so-called electrogas type and is quite similar to the equipment disclosed in detail in the aforementioned U.S. Pat. Nos. 3,382,344; 3,235,705 and 3,419,700. The basic electrogas equipment may be the basic equipment of the Vertomatic G welding machine manufactured by Arcos Corporation, 1500 South 50th Street, Philadelphia, Pa. 19143. This equipment is disclosed in some detail in an article by J. L. Hamilton, entitled Automatic Methods of Welded Tank Construction, which appeared in the Aug. 1965 issue of Welding and Metal Fabrication.

Referring to FIGS. 1 and 2, the basic welding equipment comprises front and rear positioned form shoes 104, 106, flexible conduits 108, and 112, 114 for delivering a cooling fluid (e.g. water) to, and for removing it from, internal cooling water passageways formed in the shoes 104, 106; mechanism for feeding electrode wire into the portion of the gap between plate members 24, 26 that is bounded by the upper portions of the shoes 104, 106; and supply conduit means 118 for delivering an inert gas (e.g. carbon dioxide gas) to the region of the weld pool for shielding purposes.

The means for delivering electrode wire 116 to the welding zone includes a guiding nozzle 120. According to the invention, a roll 122 of the electrode wire 116 is mounted on top of the staging 10. According to the invention, both shoes 104, 106 are mounted from frame portions of the staging 10 by means which resiliently urges the shoes 104, 106 into tight contact with the plate members 24, 26. The front shoe 104 is supported at the front end of a cradle 124 which is in turn supported by a pair of parallel swing links 126, 128. The links 126, 128 are pivotally connected at their lower ends to the cradle 124 and at their upper ends to mounting structure. A spring loaded, hand adjustable pressure screw 130 is supported behind the cradle 124 and includes an end portion 132 which bears against the rear end of cradle 124. The handle 134 of screw 130 is turned one way or the other to adjust the pressure exerted on the cradle 124 for urging the form shoe 104 against plate members 24, 26.

The support mechanism for form shoe 106 includes a yoke 136 which is pin connected at 138 to a frame portion 140 of the staging 10. A support rod 142 depends from yoke 136 and is connected at point 144 to a support member 146. A relatively thin support plate 148 is connected to member 146 and extends therefrom through the gap 150 defined by and between the two plate members 24, 26. On the side of plate members 24, 26 opposite the staging the support plate 148 is rigidly connected to an intermediate portion of an elongated support member 152. The form shoe 106 is suitably mounted to the lower end portion of member 152. As shown by FIGS. 2

and 4, a pair of rollers 154, 156 are mounted on the upper end portion of member 152 and in use contact and roll along the plate members 24, 26. A second pair of rollers 158, 160 are provided on the machine side of the plate members 24, 26. Rollers 158, 160 are journaled for rotation on the parallel leg portions 162, 164 (FIG. 4) of a mounting yoke 166. The shank portion of a pressure screw 168 extends through an opening formed in the closed end of yoke 166. The end of screw 168 is threaded and screws into a threaded bore formed in member 146. The screw 168 includes a hand knob 170. A compression spring 172 is located between the inner end of knob 170 and the outer surface of the closed end of yoke 166. Rotational movement of knob 170 rotates the screw 168 either inwardly or outwardly and this changes the amount of stored energy in spring 172, and hence the pressure exerted by such spring 172 against the yoke 166 for urging the wheels 158 into tight contact with the plate members 24, 26.

The presence and use of compression spring 172 and the compression spring urging member 132 against cradle 124 results in both shoes 104, 106 being resiliently urged or biased into tight contact against theportions of plate members 24, 26 which border the gap 150. During vertical travel of the welding machine these compression springs will be extended or contracted as necessary to maintain the shoes 104, 106 against plate members 24, 26 as the machine traverses uneven or curved sections in plate members 24, 26.

According to the invention, the welding machine is equipped with guidance mechanism which cooperates with the hold-in lines .28, 30 and their tensioning mechanisms 36, and with the support mechanism for the fonn shoes 104, 106, foradapting the weldingmachine to follow curved and/or irregular as well as substantially planar vertical surfaces during the welding operation.

As best shown by FIGS. 1 and 3-8, the guidance mechanism comprises a pair of vertically spaced apart guide wheels 174,

176, each of which is mounted to travel in the gap 150. The two wheels 174 176 are similarly mounted. Therefore, the mounting mechanism for wheel 174 will be described, with it being understood that the same type of mechanism is used for mounting wheel 176.

The wheel 174 is supported for free rotation about the shaft 178and between two collars 180, 182 which are secured to the shaft 178, such as by set screws 184.

In the illustrated embodiment one end of shaft 178 is mounted on a channel member 186 which opens laterally inwardly' of the staging 10. The opposite end of shaft 176 is mounted on a forwardly opening channel member 188 which serves as a support column for a major portion of the welding equipment. The first end of shaft 178 is secured to an end 190 of a lever arm 192. The lever arm 19-2 is pivotally mounted at a point 194.intermediate its length on a pivot pin 196. Pivot pin 196 is carried by a mounting member 198 which is secured to-a flange portion of channel member 186. The opposite end portion 200 of lever 192 projects from the pin 196 to serve as a stop for defining the limit of movement of lever arm 192, as will be further discussed below. A mounting member 202 is secured to the opposite flange of channel member 186 generally at the level of the shaft 178. A spring support-pin 204 is secured to member 202 and is surrounded by a compression spring 206. A cup 208 surrounds spring 206 and has'a closed end 210 which rests against shaft 178. The compression spring 206 bears against the inner surface of end 210.

The opposite end of shaft 178 includes a reduced diameter portion 212 which fits through a slightly oversized opening in the lower portion of a swing link 214. The upper end of link 214 includes a pin 216 which is rotatably received in a fixed sleeve 218. A compression spring. 220 is fitted on a stationary pin 222 and within a cup 224. The closed end of cup 224 bears against the shaft portion 212.

As shown by FIG. 6, the two edges of the plate'members 24, 26 at the gap are beveled to form a vee gap. The periphery of the wheels 174, 176 are laterally rounded so that the wheels will always tend to slide inwardly of the gap 150 along the sloping sides and stayjin contact with both sides of the gap 150.

As best shownby'FIGS. 7 and 8, the compression springs 206, 220 exert a biasing force on the wheels 174, 176 for normally urging them into tight contact with the side surfaces of the gap 150. When one of the guide wheels, such as guide wheel 176 (FIG. 7) for example, encounters a slight indentation in the vertical work surface, its compression springs 220 release some of their stored energy and move such guide wheel 176 away from the staging frame an amount sufficient to keep it into tight contact with the side surfaces of the gap 150. Then, as the guide wheel 176 encounters a slight crown and the other wheel 174 encounters a slight recess, the springs 220 are compressed and the springs 206 extend, so that both guide wheels 174, 176 continue in tight contact with the sidesurfaces of the gap 150. The cup and pin lengths limit the amount of forward (from the staging) movement of shaft 178 and wheel 174 and the upper end portion 200 of lever 192 limits the amount of rearward movement.

As the staging 10 climbs upwardly welding wire 16 is continuously delivered into the gap 150 in the region thereof bounded by the form shoes 104, 106. In this region the wire 116 becomes fluid and forms a molten pool which isshielded by the carbon dioxide or other inert gas being supplied to the pool region by conduit 118 and by discharge openings (not shown) in the form shoe 104. The molten metal solidifies in the region trailing the shoes 104, 106, welding the two plate members 24, 26 together.

As mentioned above, the staging 10 is driven upwardly at a rate consistent with weld deposition in the joint. One method of synchronizing the staging climbrate with weld deposition involves the use of a photoelectric cell or electric eye-232 (FIGS. 1 and 2). A suitable photoelectric cell operated control system for the-staging winch motor is disclosed by the aforementioned US. Pat. No. 3,437,786, the contents of which are hereby incorporated herein by this specific reference.

It will be understood that the embodiments described in detail hereinbefore are presented by way of example only and that changes and modifications can be made thereto without departing from the invention as his defined by the following claims.

What is claimed is:

1. A suspended staging type welding machine adapted for up and down travel along a generally vertical object at the location of a narrow vertical gap formed between spaced apart portions of said object, for welding a vertical seam at said gap, said machine comprising:

frame means;

bearing means on said frame means spaced outwardly from the vertical object;

a tensioned hold-in line contacting a rear portion of said bearing means and sloping towards said object both above and below said bearing means and exerting a holdin force on said bearing means;

means mounting said bearing means onto said frame means for movement both towards and away from said object;

reversible motorized drive means connected to said bearing means for moving the bearing means towards and away from said object, and control means for said drive means responsive to the hold-in force imposed on said bearing means by said hold-in line for causing said drive means to automatically drive said bearing means outwardly from said object whenever said force falls below a predetermined desirable value, and to automatically drive said bearing means inwardly towards said object whenever said force exceeds a predetermined value; and

1 electroslag welding equipment including a first form shoe spanning said gap on the machine side of said object, a complementary second form shoe spanning said gap on the opposite side of said object, support means securing said form shoes to said frame so that they move with said frame, and electrical means for establishing a weld puddle in said gap within the confines of said form shoes.

2. A welding machine according to claim 1, further comprising guide means for said machine including at least one wheel located on the machine side of said object, said wheel having a peripheral portion which is received by and travels in said gap, and means mounting said wheel on said frame means.

3. A welding machine according to claim 2, wherein the mounting means for the wheel comprises a horizontal shaft carrying said wheel, and means resiliently mounting said shaft on said frame means so that said shaft and the wheel carried thereby are resiliently biased towards said object but are movable relatively towards said frame means by a force capable of overcoming the biasing force.

4. A welding machine according to claim 1, wherein the support means for the second form shoe includes an elongated vertical support arm which extends upwardly from the second shoe, wheel means carried by an upper end portion of said arm, and contacting the side of said object opposite the machine, a support plate member extending from an intermediate portion of said support arm between said wheel and said second form shoe, through the gap and projecting from said object on the machine side of the object, and means securing said plate to said frame means.

5. A welding machine according to claim 4, wherein said machine further includes a second wheel means on the machine side of said object, spaced below the said first wheel, and means resiliently loading said second wheel into contact with the machine side of said object.

6. A welding machine according to claim 1, further comprising means for guiding said machine in a substantially straight line of travel relative to said gap, said means comprising first and second, vertically spaced apart, substantially coplanar guide wheels, each having a peripheral portion which is received by and rides in said gap, and means resiliently mounting said wheels on said frame means, so that said wheels are biased from said frame means towards and against said object but are free to move away relatively towards the frame means in response to a force strong enough to overcome the biasing force.

7. A welding machine according to claim 6, wherein the form shoes are vertically spaced from said guide wheels, and each shoe includes means for resiliently urging it into contact with its side of the object.

8. A welding machine according to claim 1, wherein said bearing means is a wheel having a grooved periphery for receiving said hold-in line.

9. A welding machine according to claim 1, comprising a pair of said hold-in lines, laterally spaced apart across the frame means, a said bearing means for each said hold-in line, and a said means for automatically moving the bearing means connected to each bearing means.

10. A welding machine according to claim 9, comprising reversible drive means connected to each said bearing means for moving the bearing means towards and away from said object, and control means for said drive means responsive to the hold-in force imposed on said bearing means by said hold-in line for causing said bearing means to automatically move outwardly from said object whenever said force falls below a predetermined desirable value, and to automatically move inwardly towards said object whenever said force exceeds a predetermined value.

11. A welding machine according to claim 9, comprising a separate control means for each bearing means, with each said control means functioning independently of the other by responding only to the l oldjn forcp ers erted by its hold-in line. 

1. A suspended staging type welding machine adapted for up and down travel along a generally vertical object at the location of a narrow vertical gap formed between spaced apart portions of said object, for welding a vertical seam at said gap, said machine comprising: frame means; bearing means on said frame means spaced outwardly from the vertical object; a tensioned hold-in line contacting a rear portion of said bearing means and sloping towards said object both above and below said bearing means and exerting a hold-in force on said bearing means; means mounting said bearing means onto said frame means for movement both towards and away from said object; reversible motorized drive means connected to said bearing means for moving the bearing means towards and away from said object, and control means for said drive means responsive to the holdin force imposed on said bearing means by said hold-in line for causing said drive means to automatically drive said bearing means outwardly from said object whenever said force falls below a predetermined desirable value, and to automatically drive said bearing means inwardly towards said object whenever said force exceeds a predetermined value; and electroslag welding equipment including a first form shoe spanning said gap on the machine side of said object, a complementary second form shoe spanning said gap on the opposite side of said object, support means securing said form shoes to said frame so that they move with said frame, and electrical means for establishing a weld puddle in said gap within the confines of said form shoes.
 2. A welding machine according to claim 1, further comprising guide means for said machine including at least one wheel located on the machine side of said object, said wheel having a peripheral portion which is received by and travels in said gap, and means mounting said wheel on said frame means.
 3. A welding machine according to claim 2, wherein the mounting means for the wheel comprises a horizontal shaft carrying said wheel, and means resiliently mounting said shaft on said frame means so that said shaft and the wheel carried thereby are resiliently biased towards said object but are movable relatively towards said frame means by a force capable of overcoming the biasing force.
 4. A welding machine according to claim 1, wherein the support means for the second form shoe includes an elongated vertical support arm which extends upwardly from the second shoe, wheel means carried by an upper end portion of said arm, and contacting the side of said object opposite the machine, a support plate member extending from an intermediate portion of said support arm between said wheel and said second form shoe, through the gap and projecting from said object on the machine side of the object, and means securing said plate to said frame means.
 5. A welding machine according to claim 4, wherein said machine further includes a second wheel means on the machine side of said object, spaced below the said first wheel, and means resiliently loading said second wheel into contact with the machine side of said object.
 6. A welding machine according to claim 1, further comprising means for guiding said machine in a substantially straight line of travel relative to said gap, said means comprising first and second, vertically spaced apart, substantially coplanar guide wheels, each having a peripheral portion which is received by and rides in said gap, and means resiliently mounting said wheels on said frame means, so that said wheels are biased from said frame means towards and against said object but are free to move away relatively towards the frame means in response to a force strong enough to overcome the biasing force.
 7. A welding machine according to claim 6, wherein the form shoes are vertically spaced from said guide wheels, and each shoe includes means for resiliently urging it into contact with its side of the object.
 8. A welding machine according to claim 1, wherein said bearing means is a wheel having a grooved periphery for receiving said hold-in line.
 9. A welding machine according to claim 1, comprising a pair of said hold-in lines, laterally spaced apart across the frame means, a said bearing means for each said hold-in line, and a said means for automatically moving the bearing means connected to each bearing means.
 10. A welding machine according to claim 9, comprising reversible drive means connected to each said bearing means for moving the bearing means towards and away from said object, and control means for said drive means responsive to the hold-in force imposed on said bearing means by said hold-in line for causing said bearing means to automatically move outwardly from said object whenever said force falls below a predetermined desirable value, and to automatically move inwardly towards said object whenever said force exceeds a predetermined value.
 11. A welding machine according to claim 9, comprising a separate control means for each bearing means, with each said control means functioning independently of the other by responding only to the hold-in force exerted by its hold-in line. 